1. Field of the Invention
The present invention relates to a piezoelectric resonator. More particularly, the present invention relates to an improved terminal structure for electrical connection with input and output electrodes of a three-terminal type piezoelectric resonating element.
2. Description of the Prior Art
FIG. 1 illustrates an exploded perspective view of a conventional piezoelectric resonator which is the background art for the present invention; FIG. 2 illustrates a perspective view of the appearance of a piezoelectric resonating element 4 included in the device of FIG. 1; and FIG. 3 illustrates an electric equivalent of the piezoelectric resonating element 4 as shown in FIG. 2.
Referring first to FIGS. 1 to 3, the conventional piezoelectric resonator as the background art for the present invention will be discussed. A lead frame 1 includes a tape-shaped hoop 11, "L" shaped lead portions 12 and 13 extending from the hoop and contact portions 14 and 15 at the pointed portions of the respective lead portions 12 and 13. The contact portions 14 and 15 of the lead frame 1 are housed in a base 2. The base 2 is provided with a cavity 21 for accommodation of the contact portions 14 and 15 of the lead frame 1 and terminal lead-out portions 22 and 23 for leading the lead portions 12 and 13 of the lead frame 1 out of the base 2. There is further provided at a side wall of the base 2 a withdrawing portion 24 for withdrawing a lead portion 52 of a common electrode plate 5, described below, out of the base 2. It is noted that the contact portions 14 and 15 of the lead frame 1 are accommodated within the cavity 21 in the base 2, with the lead portions 12 and 13 being withdrawn through the terminal withdrawing portions 22 and 23. There is mounted a sheet 3 of anisotropic conductive rubber on the contact portions 14 and 15. The anisotropic conductive rubber sheet 3 exhibits conductivity in a vertical direction but no conductivity in a horizontal one because of very fine stainless wires embedded in the rubber sheet in the vertical direction, for example.
Disposed over the above mentioned anisotropic conductive rubber sheet 3 is a piezoelectric resonating element 4. The piezoelectric resonating element 4, as indicated in FIG. 2, bears an input electrode 42 and an output electrode 43 on one major surface of a piezoelectric unit 41 and a whole electrode 44 on the opposite major surface thereof. A groove 45 is defined between the input electrode 42 and the output electrode 43, while grooves 46 and 47 are defined in the input electrode 42 and the output electrode 43 to prevent spurious oscillation. As seen from FIG. 3, the piezoelectric resonating element 4 behaves as a three-terminal type piezoelectric resonating element and causes longitudinal oscillation at a fundamental frequency as determined by the longitudinal length of the element. The piezoelectric resonating element 4 is mounted on the above mentioned anisotropic conductive rubber sheet 3 with the input electrode 42 and the output electrode 43 oriented downwardly. Since under these circumstances the anisotropic conductive rubber sheet 3 exhibits conductivity in the vertical direction, the input electrode 42 and the output electrode 43 of the piezoelectric resonating element 4 come into electrical contact with the contact portions 14 and 15 by way of the anisotropic conductive rubber sheet 3.
Furthermore, there is disposed the common electrode plate 5 which is in contact with the whole electrode 44 on the piezoelectric resonating element 4. The common electrode plate 5 includes a lead portion 52 extending from a hoop 51. The lead portion 52 has an "L" shaped bend portion 53 to be fitted into the terminal withdrawing portion 24 in the base 2, which bend portion 53 bears at its pointed portion a contact portion 54 so bent as to come into contact with the whole electrode 44 on the piezoelectric resonating element 4. The contact portion 54 has at its both ends press portions 55 and 56 which abut against an inner wall of a casing 6 discussed below and urge the contact portion 54 against the whole electrode 44 on the piezoelectric resonating element 4. The common electrode plate 5 is housed in the base 2 so that the contact portion 54 thereof may come to electric contact with the whole electrode 44 of the piezoelectric resonating element 4 substantially at a central node point. The unit with its components in the base 2 is inserted into the casing 6 having an opening 61 at its one side. Eventually, synthetic resin is injected through the opening 61 of the casing 6 to integrate the base 2 and the casing 6 into a single unit.
FIG. 4 is a perspective view of the piezoelectric resonator so assembled as best shown in FIG. 1.
In some instances two of the piezoelectric resonators 20 assembled as in FIG. 1 are serially connected as shown in an equivalent circuit diagram of FIG. 5, for example. In this instance it is more convenient for subsequent manipulation and assembling of the device if the two piezoelectric resonators 20 are combined into an integral unit prior to the assembling of the device. To this end, the two piezoelectric resonators 20 are adhered together, with the casing 6 of one of the resonators in close contact with the casing 6 of the other, in a conventional device of FIG. 6. In an alternative conventional device of FIG. 7, a cabinet 30 is prepared for accommodation and integration of the two piezoelectric resonators 20. The conventional devices of FIGS. 6 and 7 require the assembling of the two piezoelectric resonators 20 for integration after the makeup of the individual piezoelectric resonators 20. In the device of FIG. 7, the cabinet 30 is additionally required with attendant increase in the manufacturing cost. Another outstanding disadvantage is that the device consisting of mere adhesion of the two piezoelectric resonators 20 becomes larger in size and the device using the cabinet 30 becomes much larger by the size of the cabinet 30.